1. Field of the Invention
This invention relates generally to a method and apparatus for the control of oil and gas production wells. More particularly, this invention relates to a method and apparatus for automatically controlling petroleum production wells using downhole computerized control systems. This invention also relates to a control system for controlling production wells, including multiple zones within a single well, from a remote location. This invention further relates to a method and system for power management for downhole devices requiring electrical power.
2. The Prior Art
The control of oil and gas production wells constitutes an on-going concern of the petroleum industry due, in part, to the enormous monetary expense involved as well as the risks associated with environmental and safety issues.
Production well control has become particularly important and more complex in view of the industry wide recognition that wells having multiple branches (i.e., multilateral wells) will be increasingly important and commonplace. Such multilateral wells include discrete production zones which produce fluid in either common or discrete production tubing. In either case, there is a need for controlling zone production, isolating specific zones and otherwise monitoring each zone in a particular well. As a consequence, sophisticated computerized controllers have been positioned at the surface of production wells for control of downhole devices such as the motor valves. In addition, such computerized controllers have been used to control other downhole devices such as hydro-mechanical safety valves. These typically microprocessor based controllers are also used for zone control within a well and, for example, can be used to actuate sliding sleeves or packers by the transmission of a surface command to downhole microprocessor controllers and/or electromechanical control devices.
The surface controllers are often hardwired to downhole sensors which transmit information to the surface such as pressure, temperature and flow. This data is then processed at the surface by the computerized control system. Electrically submersible pumps use pressure and temperature readings received at the surface from downhole sensors to change the speed of the pump in the borehole. As an alternative to downhole sensors, wire line production logging tools are also used to provide downhole data on pressure, temperature, flow, gamma ray and pulse neutron using a wire line surface unit. This data is then used for control of the production well.
There are numerous prior art patents related to the control of oil and gas production wells. In general, these prior patents relate to (1) surface control systems using a surface microprocessor and (2) downhole control systems which are initiated by surface control signals.
While it is well recognized that petroleum production wells will have increased production efficiencies and lower operating costs if surface computer based controllers and downhole microprocessor controller (actuated by external or surface signals) of the type discussed hereinabove are used, the presently implemented control systems nevertheless suffer from drawbacks and disadvantages. For example, as mentioned, all of these prior art systems generally require a surface platform at each well for supporting the control electronics and associated equipment. However, in many instances, the well operator would rather forego building and maintaining the costly platform. Thus, a problem is encountered in that use of present surface controllers require the presence of a location for the control system, namely the platform. Still another problem associated with known surface control systems (wherein a downhole microprocessor is actuated by a surface signal) is the reliability of surface to downhole signal integrity. It will be appreciated that should the surface signal be in any way compromised on its way downhole, then important control operations (such as preventing water from flowing into the production tubing) will not take place as needed.
In multilateral wells where multiple zones are controlled by a single surface control system, an inherent risk is that if the surface control system fails or otherwise shuts down, then all of the downhole tools and other production equipment in each separate zone will similarly shut down leading to a large loss in production and, of course, a loss in revenue.
Still another significant drawback of present production well control systems involves the extremely high cost associated with implementing changes in well control and related workover operations. Presently, if a problem is detected at the well, the customer is required to send a rig to the wellsite at an extremely high cost (e.g.,5 million dollars for 30 days of offshore work). The well must then be shut in during the workover causing a large loss in revenues (e.g., 1.5 million dollars for a 30 day period). Associated with these high costs are the relatively high risks of adverse environmental impact due to spills and other accidents as well as potential liability of personnel at the rig site. Of course, these risks can lead to even further costs. Because of the high costs and risks involved, in general, a customer may delay important and necessary workover of a single well until other wells in that area encounter problems. This delay may cause the production of the well to decrease or be shut in until the rig is brought in.
Still other problems associated with present production well control systems involve the need for wireline formation evaluation to sense changes in the formation and fluid composition. Unfortunately, such wireline formation evaluation is extremely expensive and time consuming. In addition, it requires shut-in of the well and does not provide "real time" information. The need for real time information regarding the formation and fluid is especially acute in evaluating undesirable water flow into the production fluids.